Slow-Fast (Sf) Corner

Slow-Fast (SF) corner is the opposite of FS corner — NMOS slow while PMOS fast, completing the asymmetric corner coverage to catch timing failures on the opposite transition direction.

What Is SF Corner?

• Definition: NMOS slow + PMOS fast (or opposite convention).
• Purpose: Verify opposite edge from FS corner, complete asymmetric coverage.
• Use: Complement to FS corner for full verification.

SF Corner Characteristics

NMOS: Slow process, low mobility, high Vth.
PMOS: Fast process, high mobility, low Vth.
Result: Opposite imbalance from FS corner.

Why SF Corner Matters?

• Complete Coverage: Catches failures FS corner misses.
• Opposite Edge: Verifies the other transition direction.
• Analog Balance: Tests differential pairs from other side.
• Symmetry: Ensures both edges are verified.

What Gets Verified

Opposite Transition: Check edge not covered by FS.
Hold Time: Verify no violations on this edge.
Analog Circuits: Test from opposite imbalance direction.
Level Shifters: Verify both polarity combinations.

Applications: Complete corner coverage, analog verification, differential circuit analysis.

SF corner is the mirror image — proving every transition works even when the opposite polarity dominates.